In terms of focus, lenses can be divided into single focus lenses, bifocal lenses and multifocal lenses.
It is divided into spherical lens and aspherical lens according to lens radian.
Progressive and single focus lenses:
The most common lens is the single focus lens, which has only one luminosity; The bifocal lens is a bifocal lens, which was used by many elderly people to solve the problem of seeing far and seeing near at the same time. However, due to its major shortcomings and the gradual popularity of multi focus, the bifocal lens has been basically eliminated.
As a milestone in the history of lens development, multifocal lenses will also be the main direction of scientific research and development and market popularization in the future, and will also be a hot spot for people who buy glasses in recent years. Progressive lens is also called progressive multifocal lens. As the name implies, there are multiple focal points on one lens. Wearing progressive lenses is like taking pictures with a camera. A pair of glasses can not only see the distance, but also see the near, and also see objects at medium distance. Therefore, we also describe progressive lenses as “zoom lenses”. After wearing them, one pair of glasses is equivalent to multiple glasses.
Progressive lens advantages:
Beautiful appearance. Compared with the dual lens, the degree of the lens changes step by step, so there is no jump. Like the ordinary single lens, there is no obvious boundary.
It protects the age privacy of the wearer (for the wearer of presbyopic glasses), and there is no need to worry about revealing the age secret due to wearing glasses.
It is convenient to look far and near, and there is no need to wear glasses frequently. Clear vision can be obtained at all distances within the visual range. A pair of glasses can meet the requirements of remote use, near use and various distances in the middle at the same time. For the presbyopia population, the trouble of frequently removing and wearing glasses is avoided.
Especially suitable for teachers, doctors, musicians, computer operators, etc. Because these people not only need to see distant and near objects, but also can see objects in the middle distance, such as blackboard, music score, computer screen, most of the time. This is impossible for any lens except progressive multifocal lens.
Disadvantages of progressive lenses
The matching is difficult. The requirements for optometrists to have experience in the inspection and fitting of glasses are high, the requirements for the accuracy of lenses are high, and the requirements for processing are stricter. Many optometrists refuse or even deny progressive lenses because of professional and experience reasons, so that those who are suitable for wearing progressive lenses can not enjoy the problem of a pair of eyeglasses that are close to, far from, and near.
The short and medium distance vision is relatively narrow. Look at the object through the vision blurring area around the lens, and the object becomes blurry. Therefore, the new wearer should turn his head more and his eyes less when looking at things, and try to use the remote area, the near area, and the middle distance area to look at objects.
It takes a long time to adapt. It is necessary to change the habit of using eyes. It usually takes about one week to adapt. When wearing progressive multifocal glasses for the first time, you may experience slight dizziness, shake when walking, and be careful when moving up stairs. The new wearer should not drive immediately and do strenuous exercise. When looking close, you need to turn your eyes downward, and your eyes are slightly uncomfortable.
People not suitable for wearing multifocal lenses:
People with motor system disorders, poor balance (such as carsickness, seasickness, or similar vertigo symptoms), and inner ear dysfunction are also not suitable to wear progressive lenses, especially when fitting rigid progressive lenses.
Those who need near vision when looking up are not suitable, such as librarians, pilots, and water and electricity workers. People who need far vision when looking down are not suitable, such as construction workers.
Greater strabismus, amblyopia, high anisometropia, hypertension, motion sickness, cardiomyopathy, short neck, etc.
If the adjustment ability is normal, but there is a large exotropia, especially the amount of squint ＞ 6, it is not suitable for progressive lenses. Long term wearing of such people may cause the risk of decreased adjustment ability due to less use of regulation for a long time.
Teenagers should carefully choose progressive lenses. They need to check their visual function before they can comprehensively consider whether they need to wear progressive lenses. If teenagers wear it gradually, they need to review the adjustment function regularly every six months. If there is a significant decline in the ability to adjust, visual function training should be combined.
Spherical and aspherical lenses:
Spherical lens: when light of different wavelengths is incident at different positions on the rear lens with parallel optical axis, the spherical lens cannot focus to one point, while the aspherical lens can focus the light to one point.
Spherical lens, the lens is spherical arc, and its cross section is also arc. Spherical design is adopted to increase aberration and deformation, resulting in obvious bad phenomena such as unclear image, distorted field of view and narrow field of vision.
Aspheric lens, the lens is not spherical arc, but the edge of the lens is “cut” a little, and its cross section is flat. The design of aspheric surface corrects the image and solves the problem of distorted field of view. At the same time, the lens is lighter, thinner and flatter. In addition, it still has excellent impact resistance, which makes the wearer safe to use, but the price will be more expensive than spherical lenses.
With the change of the times and the rapid development of the economy, people require more and more high-quality glasses, which also makes the demand for progressive films and aspherical surfaces more and more large. Glasses are more like our “second eyes” than just accessories. Therefore, it is necessary for us to spend more time and energy on them. Finally, I sincerely hope that this information can help you!